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Q:
Alternator voltage
William Bowes
Morrow Bay, California
Twice in the past couple of months my alternator light
came on shortly after takeoff, and my backup B&C
alternator picked up the load. This has occurred within 20
hours on my recently overhauled engine, which included
overhauling the alternator.
What is the correct alternator voltage that I should be
seeing? My JPI 930 shows 26.5 to 26.8 volts at all RPMs. My
B&C generator puts out 25.8 volts at 1700 rpm. One opinion I
have received is that my voltage regulator is the likely reason
my alternator has dropped off the line. Any thoughts on what
my problem is, and how I should go about correcting it?
A:
The alternator voltage should be 28.0 - 28.4 volts. I
wouldn’t start with the voltage regulator. Since this
started with the overhauled engine, I would start with
looking at the wiring to the alternator, specifically the field
wire and grounds. The voltage regulator can be adjusted
easily by your mechanic.
Also I would see if the alternator drive coupler was
overhauled along with the alternator. If it is slipping, your
voltage will drop with increased loads and could cause
the system to fail. —DH
Magneto switch
Donald Kuskie, Centennial, Colorado
My E35 has the original magneto
Q: switch and feel that was working
fine. I have installed a new digital
tachometer and now can not get a
good mag check. My maintenance
folks feel it is a bad switch. Are
there any replacements to
this switch?
A:
Without specific informa
tion, I am going to
make the assumption that
you install ed a Horizon
Instru ment P-1000 or similar
P-lead driven tachometer.
There is no reason that the simple installation of
this P-lead pick-up tach should have interfered with
your original magneto switch. I suggest re-checking the
wiring, or possibly connecting the tach directly to the
magnetos instead of the switch. I also suggest performing an
“engine kill” test by turning your mag switch OFF momentarily
while at idle speed. If the engine continues to run, there is
a wiring issue or the mag switch is truly malfunctioning.
Next, temporarily remove the newly
installed tachometer wires from the
switch and see if magneto function
returns to normal.
If you are sure it is a faulty switch,
I have replaced the old style with the
standard keyed ACS or TCM Bendix
keyed magneto switch. —CB
Q:
Autopilot computer
adapter card
John Thomas
Huntsville, Alabama
I have a King autopilot (no
Flight Director) in my A36. My
avionics shop says the computer has
a P/N 065-5009-60 adapter card, and it
should have a 065-5009-06 card. Which
P/N do you think is the correct card?
I discussed your question with
A: tech support at Honeywell
Bendix King. They verified that the
adapter card that should apply to your
unit is the one that you indicate is
currently installed, P/N 065-5009-60.
—JC
68 AMERICAN BONANZA SOCIETY JANUARY 2013